Conductive pattern forming ink, conductive pattern, and wiring substrate

ABSTRACT

A conductive pattern forming ink for forming a conductive pattern on a substrate by a droplet discharge method includes: metal particles; an aqueous dispersion medium in which the metal particles are dispersed; sorbitol; and a polyglycerol compound having a polyglycerol skeleton. In the ink, H shown in the following Formula (I) is 0.20 to 0.80; 
                   H   =           OH   ⁡     (   A   )         Mw   ⁡     (   A   )         ⁢     X   ⁡     (   A   )         +         OH   ⁡     (   B   )         Mw   ⁡     (   B   )         ⁢     X   ⁡     (   B   )                   Formula   ⁢           ⁢     (   I   )                 
where OH(A) represents an average number of hydroxyl groups in one molecule of the polyglycerol compound, Mw(A) represents a weight-average molecular weight of the polyglycerol compound, X(A) represents a content of the polyglycerol compound in the conductive pattern forming ink in weight percent; and OH(B) represents the number of hydroxyl groups in one molecule of the sorbitol, Mw(B) represents a molecular weight of the sorbitol, and X(B) represents a content of the sorbitol in the conductive pattern forming ink in weight percent.

The entire disclosure of Japanese Patent Application No. 2007-319015,filed Dec. 10, 2007 is expressly incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to a conductive pattern forming ink, aconductive pattern, and a wiring substrate.

2. Related Art

Ceramic circuit substrates are widely used as circuit substrates (wiringsubstrates) on which electronic components are mounted. The ceramiccircuit substrates are substrates made of ceramic (ceramic-substrates)on which wiring lines made of metallic materials are provided. Suchceramic circuit substrates are advantageous in that internal componentsare formed in a multiple-layer manner and finished dimensions are stablebecause the ceramic constituting the substrates (ceramic substrates) aremultifunctional materials.

The ceramic circuit substrates are manufactured as follows. Acomposition including metal particles is provided on a ceramic formedbody made of a material containing ceramic particles and a binder in apattern corresponding to wiring lines (conductive patterns) to beformed, and then the ceramic formed body to which the composition hasbeen provided is degreased and fired in a sintering step.

As a method for forming a pattern on the ceramic formed body, screenprinting is widely employed. The screen printing, however, isdisadvantageous in that it is difficult to form fine wiring lines andachieve narrow pitches, and thus hardly satisfies the demand in recentyears for highly densified circuit substrates with miniaturized wiringlines (e.g., wiring lines having a line width of 60 μm or less) having anarrow pitch.

Alternatively, a droplet discharge method, what is called an ink-jetmethod, has recently been proposed as a method for forming a pattern ona ceramic formed body. In the droplet discharge method, a liquidmaterial (a conductive pattern forming ink) including metal particles isdischarged from a liquid discharge head as droplets. For example, referto JP-A-2007-84387.

In this regard, a related art conductive pattern forming ink has aproblem in that conductive fine particles are separated out from the inkfor forming a conductive pattern due to volatilization of its dispersionmedium around a droplet discharge portion of a droplet discharge head(ink-jet head) during a discharge waiting time and a long timecontinuing discharge. The deposited conductive fine particles around thedroplet discharge portion cause changing the paths of dischargeddroplets, i.e., what is called a flight curve occurs, resulting inproblems in that the droplets are hardly landed on a targeted portionand the discharge amount of the droplet is unstable. In addition, inthis case, it is difficult that a pattern formed on a substrate by usingthe related art conductive pattern forming ink has a sufficientlyuniformed thickness and width.

When a pattern is formed on a substrate by using the related art ink,cracks easily occur in the pattern in removing a dispersion medium fromthe formed pattern. As a result, disconnections easily occur in part ofthe formed conductive pattern. Particularly, such problems frequentlyoccur along with the recent development of highly densified circuitsubstrates with miniaturized wiring lines having a narrow pitch.

SUMMARY

An advantage of the present invention is to provide a conductive patternforming ink that can prevent the occurrence of cracks and disconnectionsin a formed conductive pattern, a conductive pattern exhibiting highreliability, and a wiring substrate having the conductive pattern andexhibiting high reliability.

Such advantage is achieved by the following aspects.

According to a first aspect of the invention, a conductive patternforming ink for forming a conductive pattern on a substrate by a dropletdischarge method, includes: metal particles; an aqueous dispersionmedium in which the metal particles are dispersed; sorbitol; and apolyglycerol compound having a polyglycerol skeleton.

In the ink, H shown in the following Formula (I) is 0.20 to 0.80.

$\begin{matrix}{H = {{\frac{{OH}(A)}{{Mw}(A)}{X(A)}} + {\frac{{OH}(B)}{{Mw}(B)}{X(B)}}}} & {{Formula}\mspace{14mu}(I)}\end{matrix}$where, OH(A) represents an average number of hydroxyl groups in onemolecule of the polyglycerol compound, Mw(A) represents a weight-averagemolecular weight of the polyglycerol compound, X(A) represents thecontent of the polyglycerol compound in the conductive pattern formingink in weight percent; and OH(B) represents the number of hydroxylgroups in one molecule of the sorbitol, Mw(B) represents a molecularweight of the sorbitol, and X(B) represents a content of the sorbitol inthe conductive pattern forming ink in weight percent.

Accordingly, the conductive pattern forming ink that has an excellentdischarge stability of droplets thereof and can prevent the occurrenceof cracks and disconnections in the conductive pattern that is to beformed can be obtained.

It is preferable that the X(A) and the X(B) satisfy a relation of0.5≦X(A)/X(B)≦15.

Accordingly, the conductive pattern forming ink can maintain itsespecially-excellent discharge stability for long periods of time so asto be able to more securely prevent the occurrence of cracks anddisconnections in forming a conductive pattern.

It is preferable that the X(A) be 1.0 wt % to 25 wt %.

Accordingly, the occurrence of cracks in the conductive pattern is moresecurely prevented and the viscosity of the conductive pattern formingink can be made sufficiently low, especially improving the dischargestability of the ink.

It is preferable that the X(B) be 3.0 wt % to 23 wt %.

Accordingly, the conductive pattern forming ink can haveespecially-excellent discharge stability, and the conductive patternthat is formed can be securely prevented from being damaged in a stepfor forming the conductive pattern.

It is preferable that the polyglycerol compound be polyglycerol.

This can more securely prevent the occurrence of disconnections andcracks in the conductive pattern to be formed.

It is preferable that the Mw(A) be 300 to 3000.

Accordingly, the occurrence of cracks in the pattern can be moresecurely prevented when the pattern that is formed from the conductivepattern forming ink is dried.

In the conductive pattern forming ink according to the first aspect, itis preferable that a total content of the sorbitol and the polyglycerolcompound in the conductive pattern forming ink be 4.0 wt % to 50 wt %.

Accordingly, the discharge stability of the conductive pattern formingink can be especially made excellent and the occurrence of cracks anddisconnections in forming the conductive pattern can be more securelyprevented.

It is preferable that the substrate be formed by degreasing andsintering a ceramic formed body, on which the ink is applied by thedroplet discharge method, made of a material containing ceramicparticles and a binder so as to have a sheet like shape.

The conductive pattern forming ink is preferably applied to the ceramicformed body by the droplet discharge method.

Accordingly, volatilization of the aqueous dispersion medium around adischarge portion of an ink-jet head can be more effectively suppressedand the viscosity of the ink can be made more appropriate, furtherimproving the discharge stability.

It is preferable that the conductive pattern forming ink be a colloidalliquid in which metal colloidal particles composed of the metalparticles and a dispersant adsorbing onto surfaces of the metalparticles is dispersed in the aqueous dispersion medium.

The conductive pattern forming ink of the aspect can be preferably usedfor forming a conductive pattern on such ceramic formed body.

It is preferable that the dispersant include one of hydroxy acid andsalt of hydroxy acid having in total three or more of at least one COOHgroup and at least one OH group, and the number of COOH groups be equalto or larger than the number of OH groups.

Accordingly, a finer conductive pattern in which the occurrence ofcracks and disconnections are more securely prevented can be formed.

It is preferable that the dispersant include one of mercapto acid andsalt of mercapto acid that have in total two or more of at least oneCOOH group and at least one SH group.

Accordingly, agglomeration of the metal particles in the conductivepattern forming ink is prevented, so that a finer conductive pattern inwhich the occurrence of cracks and disconnections is prevented can beformed.

It is preferable that the colloidal liquid have a pH of 6 to 11.

Accordingly, agglomeration of the metal particles in the conductivepattern forming ink is prevented, so that a finer conductive pattern canbe formed.

According to a second aspect of the invention, a conductive pattern isformed from the conductive pattern forming ink of the first aspect.

Accordingly, the conductive pattern having high reliability can beprovided.

According to a third aspect of the invention, a wiring substrate isprovided with the conductive pattern of the second aspect.

Accordingly, the wiring substrate having high reliability can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a longitudinal sectional view showing an example of a wiringsubstrate (ceramic circuit substrate) of the invention.

FIG. 2 is an explanatory diagram showing a schematic process of a methodfor manufacturing a wiring substrate (ceramic circuit substrate) shownin FIG. 1.

FIGS. 3A and 3B are explanatory diagrams for the manufacturing steps forthe wiring substrate (ceramic circuit substrate) shown in FIG. 1.

FIG. 4 is a perspective view showing a schematic configuration of anink-jet device.

FIG. 5 is a diagram for explaining an outline configuration of anink-jet head.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferable embodiments of the invention will be described below.

First Embodiment

Conductive Pattern Forming Ink

A conductive pattern forming ink according to a first embodiment of theinvention is used for forming a conductive pattern on a substrate,especially used for forming a conductive pattern by a droplet dischargemethod.

Any substrate may be used as a substrate on which a conductive patternis formed. However, in the embodiment, a ceramic substrate is employedas the substrate. Further, the first embodiment will be explained byexemplifying a case where the conductive pattern forming ink is appliedto a ceramic formed body (a ceramic green sheet) made of ceramic and amaterial containing a binder and having a sheet-like shape. Here, theceramic formed body and the ink applied to the ceramic formed bodyundergo a sintering step as described later so as to be a ceramicsubstrate and a conductive pattern respectively.

The conductive pattern forming ink will now be described. In theembodiment, a case using a dispersion liquid in which silver particlesare dispersed will be described as a typical one of dispersion liquidsin which metal particles are dispersed in an aqueous dispersion medium.

The conductive pattern forming ink (hereinafter, also referred to asmerely “ink”) contains an aqueous dispersion medium, silver particlesdispersed in the aqueous dispersion medium, a polyglycerol compoundhaving a polyglycerol skeleton, and sorbitol.

Aqueous Dispersion Medium

The aqueous dispersion medium will be first described.

In the embodiment, the “aqueous dispersion medium” is water and/or aliquid having an excellent compatibility with respect to water (a liquidwith a solubility of 30 grams or more per 100 grams of water at 25degrees Celsius). Thus the aqueous dispersion medium is composed ofwater and/or the liquid having the excellent compatibility with respectto water, but the aqueous dispersion medium mainly composed of water ispreferably used. Especially, the aqueous dispersion medium preferablycontains water at a content rate of 70 wt % or more, more preferably ata content rate of 90 wt % or more.

Examples of the aqueous dispersion medium include: water; an alcoholsolvent such as methanol, ethanol, butanol, propanol, and isopropanol;an ether solvent such as 1,4-dioxane, and tetrahydrofuran (THF); anaromatic heterocyclic compound solvent such as pyridine, pyrazine, andpyrrole; an amide solvent such as N,N-dimethylformamide (DMF), andN,N-dimethylacetamide (DMA); a nitrile solvent such as acetonitrile; andan aldehyde solvent such as acetoaldehyde. These may be used singly orin combination of two or more.

The content of the aqueous dispersion medium in the conductive patternforming ink is preferably in the range from 25 wt % to 60 wt %, morepreferably from 30 wt % to 50 wt %. Accordingly, the ink is allowed tohave a suitable viscosity and to lessen viscosity variation caused byvolatilization of the dispersion medium.

Silver Particle

The silver particles (metal particles) will now be described.

The silver particles are a main component of the conductive pattern tobe formed and provide conductivity to the conductive pattern.

The silver particles are dispersed in the ink.

The average particle diameter of the silver particles is preferably inthe range from 1 nm to 100 nm, more preferably from 10 nm to 30 nm.Accordingly, a discharge property of the ink can be improved andtherefore a fine conductive pattern can be easily formed.

The content of the silver particles (silver particles having a surfaceonto which no dispersant adsorbs) contained in the ink is preferably inthe range from 0.5 wt % to 60 wt %, more preferably from 10 wt % to 45wt %. Accordingly, disconnections of the conductive pattern can be moreeffectively prevented, being able to provide the conductive patternhaving higher reliability.

The silver particles (metal particles) are preferably dispersed in theaqueous dispersion medium as silver colloidal particles (metal colloidalparticles) having the surfaces onto which the dispersant adsorbs.Accordingly, the dispersibility of the silver particles with respect tothe aqueous dispersion medium is improved, especially improving thedischarge property of the ink.

The dispersant is not particularly limited, but preferably includeshydroxyl acid or its salt in which three or more of COOH groups and OHgroups in total are included, and the number of COOH groups is same asthat of OH groups or more than that. The dispersant adsorbs onto thesurfaces of the silver particles so as to form colloidal particles, andevenly disperses the silver colloidal particles in the aqueous solutionby electrical repulsion of COOH groups present in the dispersion mediumso as to stabilize a colloidal liquid. Thus the silver colloidalparticles are stably present in the ink, making it easier to form a fineconductive pattern. In addition, the silver particles are evenlydispersed in the pattern (precursor) formed from the ink, so thatcracks, disconnections, and the like do not easily occur. On the otherhand, if the total number of COOH groups and OH groups is less thanthree, or the number of COOH groups is less than that of OH groups,sufficient dispersibility of the silver colloidal particles sometimescan not be obtained.

Examples of such dispersant include: citric acid, malic acid, trisodiumcitrate, tripotassium citrate, trilithium citrate, ammonium citratetribasic, disodium malate, tannic acid, gallotannic acid, and gallnuttannin. These may be used singly or in combination of two or more.

Alternatively, mercapto acid or its salt having two or more of COOHgroups and SH groups in total may be included in the dispersant. Thedispersant forms colloidal particles by the adsorption of mercaptogroups onto the surfaces of the silver particles, and evenly dispersesthe colloidal particles in the aqueous solution by electrical repulsionof COOH groups present in the dispersion medium so as to stabilize acolloidal liquid. Thus the silver colloidal particles are stably presentin the ink, making it easier to form a fine conductive pattern. Inaddition, the silver particles are evenly dispersed in the pattern(precursor) formed from the ink, so that cracks, disconnections, and thelike do not easily occur. On the other hand, if the total number of COOHgroups and SH groups in the dispersant is less than two, that is, onlyeither one of a COOH group and a SH group is present, sufficientdispersibility of the silver colloidal particles sometimes can not beobtained.

Examples of such dispersant includes: mercaptoacetic acid,mercaptopropionic acid, thiodipropionic acid, mercaptosuccinic acid,thioacetic acid, sodium mercaptoacetate, sodium mercaptopropionate,sodium thiodipropionate, disodium mercaptosuccinate, potassiummercaptoacetate, potassium mercaptopropionate, potassiumthiodipropionate, and dipotassium mercaptosuccinate. These may be usedsingly or in combination of two or more.

The content of the silver colloidal particles in the ink is preferablyin the range from about 1 wt % to about 60 wt %, more preferably fromabout 10 wt % to about 50 wt %. If the content of the silver colloidalparticles is less than the lower limit of the range described above, theink needs to be additionally applied more than once because of a smallcontent of silver in a case where a relatively thick film is formed informing the conductive pattern. On the other hand, if the content of thesilver colloidal particles exceeds the upper limit of the range above,the dispersibility is decreased because of a large content of silver. Inthis case, the frequency of stirring needs to be increased so as toprevent the decrease of the dispersibility.

The loss on heating, up to 500 degrees Celsius in the thermogravimetricanalysis, of the silver colloidal particles is preferably from about 1wt % to about 25 wt %. If colloidal particles (solid content) are heatedup to 500 degrees Celsius, the dispersant adsorbing onto the surfaces, areducing agent (residual reducing agent) described later, and the likeare oxidized and decomposed so as to be mostly gasified and disappear.An amount of the residual reducing agent is seemed to be small, so thatit is considered that the loss on heating up to 500 degrees Celsiusnearly corresponds to the amount of the dispersant adsorbing on thesilver colloidal particles. If the loss on heating is less than 1 wt %,the dispersibility of the silver particles is decreased due to a smallamount of the dispersant with respect to the silver particles. On theother hand, if the loss on heating exceeds 25 wt %, specific resistanceof the conductive pattern is increased due to a large amount of residualdispersant with respect to the silver particles. Here, the specificresistance can be improved to some extent in such manner that theconductive pattern is heated and sintered after it is formed so as todecompose and dissipate an organic component thereof. Therefore, largerimproving effect can be obtained in a case of a ceramic substrate, forexample, that is sintered in higher temperature.

Forming of the silver colloidal particles will be described later.

Sorbitol

The conductive pattern forming ink of the first embodiment containssorbitol.

Sorbitol has an excellent moisture-retaining property, and contributesto prevention of volatilization of the dispersion medium of theconductive pattern forming ink. Therefore, the conductive patternforming ink containing sorbitol can prevent the volatilization of thedispersion medium contained therein so as to prevent increase of theviscosity thereof, even if the ink is preserved for long periods oftime. Accordingly, the conductive pattern forming ink can keep itsexcellent discharge stability for long periods of time.

In addition, sorbitol has a function to control wetness. Therefore,after the aqueous dispersion medium in the pattern (precursor of theconductive pattern described in detail later) formed from the conductivepattern forming ink is removed, sorbitol can maintain a constantconcentration level of the aqueous dispersion medium in the patternhaving been formed. That is, the pattern slightly absorbs moisture afterthe aqueous dispersion medium is removed. Here, for example, a portionhaving a large surface area in the pattern is easy to absorb moisture inthe air. However, since the pattern includes sorbitol, the moisture thathas been absorbed is rapidly dispersed in the pattern. Therefore, themoisture is prevented from converging on a part of the pattern, thusmaking the concentration level of the aqueous dispersion medium in thepattern constant. As a result, the pattern is uniformly sintered in thesintering step, providing the conductive pattern having less variationin thickness, width, and the like.

Further, sorbitol can reduce variation of the concentration level of theaqueous dispersion medium remaining in the pattern among the patternshaving been formed. That is, even when the amount of the aqueousdispersion medium remaining in the pattern varies among a plurality ofpatterns after the aqueous dispersion medium of the pattern formed fromthe ink is removed, the pattern having the aqueous dispersion mediumremoved rapidly absorbs moisture and the amount of the aqueousdispersion medium is adjusted among the patterns, thereby making theamount of the aqueous dispersion medium even among the patterns.Therefore, when the pattern that is formed is sintered, sinteringconditions such as a temperature rising condition are easily set. As aresult, volatilizing behavior of the aqueous dispersion medium among thepatterns is easily controlled. Accordingly, the occurrence of bubbles inthe sintering caused by rapid vaporization of moisture contained in theformed pattern can securely prevented. As a result, the conductivepattern can be prevented from being damaged by the bubbles produced.Further, individual difference between the formed conductive patterns isreduced.

Further, sorbitol easily burns due to its large number of oxygen permolecular weight, thereby being more easily removed (oxidized anddecomposed) from the conductive pattern in forming the conductivepattern. Further, the concentration of the sorbitol increases as theaqueous dispersion medium volatizes in drying (removing the dispersionmedium) the pattern (precursor) formed from the conductive patternforming ink. Thus the viscosity of the precursor of the conductivepattern is increased, securely preventing the ink constituting theprecursor from flowing to an undesired region. Consequently, theconductive pattern can be formed to have a desired shape with a highdegree of accuracy.

Sorbitol is also relatively hard to crystallize. Therefore, sorbitol ishardly separated out as a crystal when the aqueous dispersion medium isremoved from the conductive pattern forming ink. Therefore, when theconductive pattern is formed, the conductive pattern to be formed ishardly damaged due to the crystal of sorbitol separated out.

In addition, sorbitol has a large number of hydroxyl groups in amolecule. Further, as described above, sorbitol is relatively hard tocrystallize. Therefore, in the conductive pattern forming ink includingthe aqueous dispersion medium, sorbitol has molecules which hardlyinteract with each other, and is thus easy to be uniformly distributed.Therefore, sorbitol is easy to enter between other components in theink. Resulting from existence of sorbitol between the other components,the pattern (precursor) formed form the conductive pattern forming inkcan slightly maintain its fluidity even after the aqueous dispersionmedium is removed. Therefore, the polyglycerol compound as describedlater can favorably flow and thus favorably prevent cracks anddisconnections occurring in the conductive pattern.

A content X(B) of sorbitol in the conductive pattern forming ink ispreferably 3.0 wt % to 23 wt %, more preferably 5.0 wt % to 20 wt %.This can more securely prevent the volatilization of the aqueousdispersion medium of the conductive pattern forming ink, whereby theconductive pattern forming ink exhibits excellent discharge stabilityfor a longer period of time. If the content of sorbitol contained in theink is less than the lower limit of the range mentioned above, themoisture-retaining property of the ink sometimes can not sufficientlyincrease depending on a composition of the ink. On the other hand, ifthe content exceeds the upper limit of the range, sorbitol easilyremains in the pattern in the sintering because of its excessive-largeamount with respect to the silver particles. As a result, specificresistance of the conductive pattern is increased. The specificresistance can be improved to some extent by controlling the sinteringtime and the sintering environment. However, sorbitol is rapidlydecomposed and removed at a certain temperature, so that rapid volumeconstriction occurs depending on a temperature condition in thesintering. The rapid volume constriction may generate cracks, causingconductivity failures in some cases.

Polyglycerol Compound

The polyglycerol compound prevents the occurrence of cracks in a patternwhen the pattern (precursor of the conductive pattern described indetail later) formed from the conductive pattern forming ink is dried(the dispersion medium is removed). This can be considered as follows.If the conductive pattern forming ink contains the polyglycerolcompound, polymer chains are present between the silver particles (metalparticles), and thus the polyglycerol compound can maintain a distancebetween the silver particles. Further, since the boiling point of thepolyglycerol compound is relatively high, the compound is not removed inremoving the aqueous dispersion medium, and adsorbs onto thecircumference of the silver particles. Consequently, a state that thepolyglycerol compound wraps around the silver particles is kept for longperiods of time in removing the aqueous dispersion medium, so that rapidvolume constriction caused by the volatilization of the aqueousdispersion medium can be avoided and the grain growth (agglomeration) ofsilver can be prevented, suppressing the occurrence of cracks in thepattern.

Further, the polyglycerol compound can prevent occurrence ofdisconnections in the sintering in a process of forming the conductivepattern. This can be considered as follows. The polyglycerol compoundhas a relatively high boiling point or a relatively high decompositiontemperature. Therefore, in the process of forming the conductive patternfrom the conductive pattern forming ink, the polyglycerol compound canbe evaporated or thermally (oxidatively) decomposed after the aqueousdispersion medium is evaporated.

Further, the polyglycerol compound is present around the silverparticles until the polyglycerol compound is evaporated or thermally(oxidatively) decomposed, so as to suppress approach and agglomerationof the silver particles. After the polyglycerol compound is decomposed,the silver particles can be bonded to each other more evenly.

Since the polymer chains (polyglycerol compound) are present between thesilver particles (metal particles) in the sintering, the polyglycerolcompound can maintain a distance between the silver particles. Further,the polyglycerol compound has an appropriate fluidity. Therefore, if theink contains the polyglycerol compound, the precursor of the conductivepattern favorably follows expansion and constriction caused by thetemperature change of the ceramic formed body.

Thus the occurrence of disconnections in the conductive pattern that isformed can be prevented.

In particular, existence of sorbitol around the polyglycerol compound asdescribed above can improve fluidity of the conductive pattern formingink including the polyglycerol compound, and the pattern can furtherfavorably follow the expansion and constriction as described above. As aresult, occurrence of cracks and disconnections is more securelyprevented.

Further, the polyglycerol compound prevents sorbitol described abovefrom crystallizing. Therefore, even though the ink contains sorbitol,sorbitol is more securely prevented from crystallizing in the process offorming the conductive pattern described later so as to prevent damageof the formed conductive pattern. This is seemed to be caused by thatsince sorbitol and the polyglycerol compound that have many hydroxylgroups each other have high affinity to each other, the polyglycerolcompound can penetrate between a plurality of molecules of sorbitol soas to prevent sorbitol from crystallizing.

Further, the ink contains such polyglycerol compound, so that theviscosity of the ink can be made appropriate, more effectively improvingthe discharge stability of the ink from the ink-jet head. In addition,the film-forming property also can be improved.

Examples of the polyglycerol compound may include polyglycerol,polyglycerol ester, and the like that have a polyglycerol skeleton.These may be used singly or in combination of two or more. Examples ofpolyglycerol ester include: polyglycerol monostearate, polyglyceroltristearate, polyglycerol tetrastearate, polyglycerol monooleate,polyglycerol pentaoleate, polyglycerol monolaurate, polyglycerolmonocaprylate, polyglycerol polycinoleate, polyglycerol sesquistearate,polyglycerol decaoleate, and polyglycerol sesquioleate.

Polyglycerol is preferably used among the above. Polyglycerol isparticularly high affinity for sorbitol. Therefore, according to theadvantageous effect described above, fluidity in the ink becomessufficiently high. Consequently, when the pattern that is formed fromthe ink is dried and sintered, the pattern can have sufficiently highfluidity, and thus the occurrence of disconnections and cracks can bemore securely prevented. Further, polyglycerol is preferably usedbecause of its high solubility with respect to the aqueous dispersionmedium.

The polyglycerol compound preferably has a weight-average molecularweight in the range from 300 to 3000, more preferably from 400 to 1000,further more preferably from 400 to 600. Consequently, the occurrence ofcracks can be more securely prevented when the pattern that is formedfrom the conductive pattern forming ink is dried. In addition, thepolyglycerol compound shows high affinity for sorbitol, resulting inkeeping the pattern formed from the ink in a high fluidity for longperiods of time in the sintering. As a result, the pattern favorablyfollows the expansion and constriction caused by the temperature changeof the ceramic formed body, and occurrence of disconnections is furthersecurely prevented. If the weight-average molecular weight of thepolyglycerol compound is lower than the lower limit of the rangedescribed above, the polyglycerol compound tends to be easily decomposedwhen the aqueous dispersion medium is removed, decreasing the effectpreventing the occurrence of cracks. If the weight-average molecularweight of the polyglycerol compound exceeds the upper limit of the rangeabove, the solubility and the dispersibility in the ink are sometimesdecreased due to a removing volume effect and the like.

A content X(A) of the polyglycerol compound in the conductive patternforming ink is preferably 1.0 wt % to 25 wt %, more preferably 3.0 wt %to 19 wt %. Accordingly, the occurrence of cracks and disconnections inthe conductive pattern are more securely prevented and the viscosity ofthe ink can be made sufficiently low, especially improving the dischargestability of the ink. If the content of the polyglycerol compound islower than the lower limit of the range above and the molecular weightis lower than the lower limit, the effect preventing the occurrence ofcracks is sometimes decreased. If the content of the polyglycerolcompound exceeds the upper limit of the range above and the molecularweight exceeds the upper limit, the dispersibility of the polyglycerolcompound in the ink is sometimes decreased, and therefore it sometimesbecomes hard to sufficiently decrease the viscosity of the ink.

In the invention, the conductive pattern forming ink contains sorbitoland the polyglycerol compound such that H shown in Formula (I) is in therange from 0.20 to 0.80.

$\begin{matrix}{H = {{\frac{{OH}(A)}{{Mw}(A)}{X(A)}} + {\frac{{OH}(B)}{{Mw}(B)}{X(B)}}}} & {{Formula}\mspace{14mu}(I)}\end{matrix}$(In the formula, OH(A)[piece] represents an average number of hydroxylgroups in one molecule of the polyglycerol compound, Mw(A) represents aweight-average molecular weight of the polyglycerol compound, X(A)[wt %]represents a content of the polyglycerol compound in the conductivepattern forming ink; and OH(B)[piece] represents a number of hydroxylgroups in one molecule of sorbitol, Mw(B) represents a molecular weightof sorbitol, and X(B)[wt %] represents a content of sorbitol in theconductive pattern forming ink.)

As described above, sorbitol has the excellent moisture-retainingproperty. Further, the polyglycerol compound also has a relatively highmoisture-retaining property. It is considered that themoisture-retaining property of these components heavily depends on theamount of hydroxyl groups. Therefore, the amount of hydroxyl groups ofsorbitol and the polyglycerol compound can be a barometer of the dryingproperty of the conductive pattern forming ink. If H shown in Formula(I) is in the range described above, the aqueous dispersion medium isnot easily volatilized, whereby the conductive pattern forming inkexhibits excellent discharge stability. That is, the ink is preventedfrom increasing its viscosity and being dried around the dischargeportion, exhibiting excellent discharge stability of droplets thereof.That is, variation in weight of droplets of the ink is small, resultingin little clogging and little flying failure. Consequently, a patternhaving an even thickness and even width can be easily formed from theink, so that the resulting conductive pattern has an even thickness andan even width and hardly has cracks, disconnections, and the like. Inparticular, even in a case where the inkjet device having the conductivepattern forming ink supplied thereto is left for a predetermined periodof time (e.g. 5 days) without being operated, the conductive patternforming ink according to the invention is accurately discharged in atarget position in a uniform amount.

Further, only a little amount of the aqueous dispersion medium in theconductive pattern forming ink volatilizes, enabling the conductivepattern forming ink to exhibit little variation in properties such asviscosity and thus achieving an excellent stability.

Further, if H is in the range described above, the moisture-retainingproperty of the conductive pattern forming ink can be prevented fromextremely increasing. Accordingly, when the conductive pattern formingink is applied on a ceramic formed body and the aqueous dispersionmedium is removed, moisture residual in the pattern (precursor) that isformed can be made sufficiently small. Further, the pattern can beprevented from absorbing moisture, even after the aqueous dispersionmedium is removed. Consequently, occurrence of bubbles formed from theaqueous dispersion medium can be securely prevented in the sintering soas to be able to prevent damage of the conductive pattern that isformed.

From the advantageous effects described above, the conductive patternformed from the conductive pattern forming ink is prevented from havingcracks, disconnections, and the like, and the ink exhibits excellentdischarge stability. Therefore, the conductive pattern formed from suchink is highly reliable.

If H shown in Formula (I) is lower than the lower limit of the rangedescribed above, the aqueous dispersion medium in the ink is easilyvolatilized because of low amount of hydroxyl groups in the ink.Consequently, in a case where the ink is discharged for long periods oftime or in a case where the ink is put and left in the ink-jet devicefor long periods of time, the dispersion medium of the conductivepattern forming ink around the discharge portion is easily volatilizedso as to increase the viscosity of the ink around the discharge portion.If the viscosity of the ink is increased or the silver particles areagglomerated around the discharge portion, the paths of dischargeddroplets vary, i.e., what is called a flight curve occurs), resulting inproblems in that the droplets are hardly landed on targeted positionsand the discharge amount of the droplets is unstable. As a result, thepattern formed from the ink that is discharged on the ceramic formedbody has an uneven thickness and an uneven width, so that cracks anddisconnections easily occur from a portion having a small thickness anda portion having a small width.

On the other hand, if H shown in Formula (I) exceeds the upper limit ofthe range above, the moisture-retaining property of the conductivepattern forming ink becomes too high. Therefore, when the conductivepattern forming ink is applied to the ceramic formed body and theaqueous dispersion medium is removed, a large amount of aqueousdispersion medium is left in the formed pattern (precursor).Consequently, when the pattern is sintered, the aqueous dispersionmedium rapidly vaporizes so as to produce bubbles. The produced bubblesdamage the pattern, causing many cracks and disconnections of the formedconductive pattern. Further, organic substance contained in theconductive pattern forming ink is excessively increased, making it hardthat the silver particles bond to each other in the sintering.Furthermore, the moisture-retaining property of the ink becomesexcessively high and a fluidity of the pattern formed from the inkbecomes high, making it hard to draw a fine pattern. Further, a binderof the ceramic formed body on which the ink is applied is commonlyhydrophobic. In such case, adhesiveness between the ink and the ceramicformed body is lowered. Therefore, the pattern (precursor) is easilypeeled off from the ceramic formed body or the disconnection easilyoccurs in a laminating or sintering step of the ceramic formed bodydescribed later. Consequently, the conductive pattern having highreliability can not be obtained.

H shown in Formula (I) is in the range described above, but preferablyin the range from 0.25 to 0.65, more preferably in the range from 0.30to 0.60, more prominently providing the advantageous effect describedabove.

Here, in this specification, OH(A)[piece] represents the average numberof hydroxyl groups in one molecule in the polyglycerol compound. Theaverage number of hydroxyl groups is calculated by the weighted averagebased on the molecular weight of the polyglycerol compound.

As described above, the conductive pattern forming ink according to thefirst embodiment of the invention contains sorbitol and the polyglycerolcompound. In a case where the ink contains only either one of sorbitolor the polyglycerol compound, the advantageous effect of the inventioncan not be obtained.

In a case where the ink contains no sorbitol, the aqueous dispersionmedium in the ink easily volatilizes, decreasing the discharge stabilityof droplets of the ink. Further, in this case, since the fluidity of thepolyglycerol compound is not maintained sufficiently high, the effect toprevent disconnections and cracks may not be sufficiently obtaineddepending on a type of the polyglycerol compound. Alternatively, the inkcontains a large amount of polyglycerol compound instead of sorbitol andH may be made to be in the range described above. However, in this case,the ink contains too many organic substances, increasing the viscosityof the ink. Consequently, the discharge stability of droplets of the inkis decreased.

Further, in a case where the polyglycerol compound is not included inthe ink, when the pattern formed from the ink is sintered, the patternis broken due to thermal expansion of the ceramic formed body on whichthe pattern is formed, causing many disconnections in the conductivepattern that is formed. Consequently, it becomes hard to obtain aconductive pattern having high reliability. Further, depending on theconditions for drying or sintering, sorbitol may be crystallized.Therefore, in some cases, the pattern to be formed is damaged by thecrystals generated in the pattern.

Furthermore, X(A) and X(B) preferably satisfy 0.10≦X(A)/X(B)≦15, morepreferably 0.50≦X(A)/X(B)≦8. Accordingly, the viscosity of the ink stayssufficiently low, particularly improving the discharge stability of theink over long periods. Further, an amount of the moisture in the patternafter drying can be sufficiently lowered while the moisture-retainingproperty of the ink is made appropriate, whereby occurrence of cracks,disconnections, and the like can be more securely prevented in formingthe conductive pattern.

The total content of sorbitol and the polyglycerol compound in theconductive pattern forming ink is preferably 4.0 wt % to 50 wt %, morepreferably 8.0 wt % to 40 wt %. Accordingly, the viscosity of the inkcan be made sufficiently low and the aqueous dispersion medium in theink can be more securely prevented from volatilizing, especiallyimproving the discharge stability of droplets of the ink. As a result,the occurrence of disconnections, cracks, and the like in the formedconductive pattern can be more securely prevented. Further, themoisture-retaining property of the conductive pattern forming ink can bemore easily adjusted, so that the aqueous dispersion medium of thepattern (precursor) that is formed from the ink can be more easilyremoved.

Other Component

Further, the conductive pattern forming ink may contain an acetyleneglycol based compound as well as the above-mentioned components. Theacetylene glycol based compound adjusts a contact angle between theconductive pattern forming ink and the ceramic formed body so as to setthe angle to be in a predetermined range. In addition, a small additiveamount of the acetylene glycol based compound can adjust the contactangle between the conductive pattern forming ink and the ceramic formedbody so as to set the angle to be in the predetermined range. Further,even if bubbles are mixed in discharged droplets, the bubbles can beremoved promptly.

The contact angle between the conductive pattern forming ink and theceramic formed body is thus adjusted to be in the predetermined range,being able to form a finer conductive pattern.

The compound described above, in particular, adjusts the contact anglebetween the conductive pattern forming ink and the ceramic formed bodyto set it to be in the range from 40 degrees to 80 degrees (morepreferably, 50 degrees to 80 degrees). If the contact angle is toosmall, it sometimes becomes hard to form a conductive pattern having afine line width. On the other hand, if the contact angle is too large,it sometimes becomes hard to form a conductive pattern having an evenline width depending on discharging conditions. Further, it sometimeshappens that a contact area between landed droplets and the ceramicformed body is too small, and therefore the landed droplets are out oflanding positions.

Examples of the acetylene glycol based compound include: Surfynol 104series (104E, 104H, 104PG-50, 104PA, and the like), Surfynol 400 series(420, 465, 485, and the like), and Olfine series (EXP4036, EXP4001,E1010, and the like) (“Surfynol” is a product name of Air Products andChemicals, Inc. and “Olfine” is a product name of Nissin ChemicalIndustry Co., Ltd). These may be used singly or in combination of two ormore.

The ink preferably contains two or more kinds of acetylene glycol basedcompounds having different hydrophile-lipophile balance (HLB) valuesfrom each other. Accordingly, the contact angle between the conductivepattern forming ink and the ceramic formed body can be more easilyadjusted to be in the predetermined range.

Especially, among two or more of acetylene glycol based compoundscontained in the ink, the difference between an HLB value of theacetylene glycol based compound having the highest HLB value and an HLBvalue of the compound having the lowest HLB value is preferably in therange from 4 to 12, more preferably from 5 to 10. Accordingly, with asmaller additive amount of the acetylene glycol based compound, thecontact angle between the conductive pattern forming ink and the ceramicformed body can be adjusted so as to be in the predetermined range.

In a case where the ink containing two or more kinds of acetylene glycolbased compounds is used, the HLB value of the acetylene glycol basedcompound having the highest HLB value is preferably in the range from 8to 16, more preferably from 9 to 14.

In addition, in a case where the ink containing two or more kinds ofacetylene glycol based compounds is used, the HLB value of the acetyleneglycol based compound having the lowest HLB value is preferably in therange from 2 to 7, more preferably from 3 to 5.

The content of the acetylene glycol based compound contained in the inkis preferably in the range from 0.001 wt % to 1 wt %, more preferably0.01 wt % to 0.5 wt %. Accordingly, the contact angle between theconductive pattern forming ink and the ceramic formed body can be moreeffectively adjusted to be in the predetermined range.

Furthermore, the conductive pattern forming ink may contain1,3-propanediol as well as the above-mentioned components. Accordingly,the volatilization of the aqueous dispersion medium around the dischargeportion of the ink-jet head can be more effectively suppressed and theviscosity of the ink can be made more appropriate, further improving thedischarge stability.

In a case where the ink contents 1,3-propanediol, the content of it ispreferably 0.5 wt % to 20 wt %, more preferably 2 wt % to 10 wt %.Accordingly, the discharge stability of the ink can be more effectivelyimproved. In addition, the crystallization of sorbitol can be moresecurely prevented in the forming of the conductive pattern.

For example, the conductive pattern forming ink may contain polyalcoholsuch as ethylene glycol, 1,3-butylene glycol, 1,3-propanediol, propyleneglycol, and sugar alcohol obtained by reducing aldehyde groups andketone group of sugar.

Among them, especially, in a case where the conductive pattern formingink contains at least one of maltitol and lactitol, sorbitol can be moresecurely prevented from crystallizing.

Further, the ink may contain water-soluble polymer such as polyethyleneglycol and polyvinyl alcohol. Examples of polyethylene glycol include:polyethylene glycol #200 (weight-average molecular weight of 200),polyethylene glycol #300 (weight-average molecular weight of 300),polyethylene glycol #400 (weight-average molecular weight of 400),polyethylene glycol #600 (weight-average molecular weight of 600),polyethylene glycol #1000 (weight-average molecular weight of 1000),polyethylene glycol #1500 (weight-average molecular weight of 1500),polyethylene glycol #1540 (weight-average molecular weight of 1540), andpolyethylene glycol #2000 (weight-average molecular weight of 2000).Examples of polyvinyl alcohol include: polyvinyl alcohol #200(weight-average molecular weight of 200), polyvinyl alcohol #300(weight-average molecular weight of 300), polyvinyl alcohol #400(weight-average molecular weight of 400), polyvinyl alcohol #600(weight-average molecular weight of 600), polyvinyl alcohol #1000(weight-average molecular weight of 1000), polyvinyl alcohol #1500(weight-average molecular weight of 1500), polyvinyl alcohol #1540(weight-average molecular weight of 1540), and polyvinyl alcohol #2000(weight-average molecular weight of 2000). These may be singly or incombination of two or more.

Second Embodiment

Method for Producing Conductive Pattern Forming Ink

An example of a method for producing a conductive pattern forming inksuch as the ink described above will now be described as a secondembodiment of the invention.

In the second embodiment, the conductive pattern forming ink is acolloidal liquid obtained by dispersing silver colloidal particles in anaqueous dispersion medium.

In producing a conductive pattern forming ink, an aqueous solution inwhich a dispersant and a reducing agent are dissolved is first prepared.

The dispersant is preferably blended in such amount that a molar ratiobetween silver of silver salt such as silver nitrate which is a startingsubstance and the dispersant is set to be about 1:1 to about 1:100. Ifthe molar ratio of the dispersant with respect to silver salt isincreased, a particle diameter of the silver particles is decreased.Therefore, contact points between the particles in the formed conductivepattern are increased, being able to obtain a film having a lowvolume-resistance value.

The reducing agent reduces Ag⁺ ions in silver salt such as silvernitrate (Ag⁺NO³⁻) which is a starting substance so as to produce silverparticles.

The reducing agent is not especially limited. Examples of the reducingagent include: amins such as hydrazine, dimethylaminoethanol,methyldiethanolamine, and triethanolamine; hydrogen compounds such assodium borohydride, hydrogen gas, and hydrogen iodide; oxides such ascarbon monoxide, sulfurous acid, and hypophosphite; low-valent metalsalts such as Fe(II) compound, and Sn(II) compound; sugars such asD-glucose; organic compounds such as formaldehyde; hydroxy acids such ascitric acid, and malic acid; hydroxyl acid salts such as trisodiumcitrate, tripotassium citrate, trilithium citrate, ammonium citratetribasic, and disodium malate; and tannic acids. Among these, tannicacids and hydroxyl acids function not only as the reducing agent butalso the dispersant so as to be preferably used. Preferable examples ofthe dispersant for forming a stable bond on surfaces of metals include:mercapto acids such as mercaptoacetic acid, mercaptopropionic acid,thiodipropionic acid, mercaptosuccinic acid, and thioacetic acid; andmercaptoacid salts such as sodium mercaptoacetate, sodiummercaptopropionate, sodium thiodipropionate, sodium mercaptosuccinate,potassium mercaptoacetate, potassium mercaptopropionate, potassiumthiodipropionate, and potassium mercaptosuccinate. These dispersants andreducing agents may be used singly or in combination of two or more.When any of these compounds is used, the reduction reaction may bepromoted with light or heat.

The reducing agent should be blended in such amount that the agent cancompletely reduce silver salt which is the starting substance. However,it should be blended at a minimum necessary amount, because if thereducing agent is blended excessively, it remains in the silvercolloidal liquid as an impurity, causing deterioration of theconductivity after film forming. Specifically, the reducing agent isblended such that a molar ratio between silver salt and the reducingagent is about 1:1 to about 1:3.

In the second embodiment, after the aqueous solution is prepared bydissolving the dispersant and the reducing agent, a pH of the aqueoussolution is preferably adjusted to be 6 to 12.

This is because of the following reasons. For example, in a case wheretrisodium citrate serving as the dispersant and ferrous sulfate servingas the reducing agent are blended, a pH is about 4 to about 5, that is,lower than 6 which is described above, though it varies depending on thewhole concentration. In this case, hydrogen ions shift the equilibriumof the reaction expressed by the following Formula (1) to the right sideof the formula, increasing the amount of COOH. Therefore, the electricalrepulsion of the surfaces of the silver particles that are obtained bydelivering a silver salt solution by drops into the aqueous solutionafter this mixing is reduced, reducing the dispersibility of the silverparticles (colloidal particles).—COO⁻+H⁺→—COOH  Formula (1)

Because of this, after the aqueous solution is prepared by dissolvingthe dispersant and the reducing agent, an alkaline compound is added tothe aqueous solution so as to decrease the concentration of hydrogenions.

The alkaline compound that is added is not especially limited, butsodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia water,and the like can be used. Among these, sodium hydroxide that can easilyadjust a pH in small amounts is preferably used.

Here, if a pH exceeds 10 by adding the alkaline compound too much,hydroxide of ions, such as ferric ions, of the reducing agent thatremains is easily precipitated.

Next, an aqueous liquid containing silver salt is delivered by dropsinto the aqueous solution in which the dispersant and the reducing agentthat are prepared are dissolved.

Silver salt is not especially limited but may be silver acetate, silvercarbonate, silver oxide, silver sulfate, silver nitrite, silverchlorate, silver sulfide, silver chromate, silver nitrate, silverdichromate, for example. Among these, silver nitrate having highsolubility with respect to water is preferably used.

Further, the amount of silver salt is determined in view of a desiredcontent of the colloidal particles and a desired reducing ratio by thereducing agent. In a case of silver nitrate, the amount is preferablyabout 15 pts.wt to about 70 pts.wt with respect to the aqueous solutionof 100 pts.wt.

The silver salt aqueous solution is prepared by dissolvingabove-described silver salt in purified water. Then the silver saltaqueous solution is gradually delivered by drops into the aqueoussolution in which the dispersant and the reducing agent described aboveare dissolved.

In this step, silver salt is reduced by the reducing agent and thedispersant adsorbs onto surfaces of the silver particles so as to formsilver colloidal particles. Thus an aqueous solution in which the silvercolloidal particles are dispersed is obtained.

The resulting solution contains residues of the reducing agent and thedispersant as well as the colloidal particles, showing a high ionicconcentration. In the liquid in such state, coagulation andprecipitation easily occur. Therefore, washing is preferably conductedso as to remove extra ions in the aqueous solution and decrease theionic concentration.

As a method of washing, the following steps are repeated several times,for example: leaving the aqueous solution containing the colloidalparticles at rest for a certain period, removing a supernatant solutionthat is produced from the aqueous solution, adding purified water to thesolution and stirring the solution again, further leaving the solutionat rest for a certain period, removing a newly produced supernatantsolution. A method in which centrifugal separation is conducted insteadof the leaving at rest, and a method in which ions are removed byultrafiltration may be also used.

Alternatively, the following method may be used for washing. After thesolution is produced, a pH of the solution is adjusted to be in an acidrange that is 5 or less, and the electrical repulsion of the surfaces ofthe silver particles is reduced by shifting the equilibrium of thereaction expressed in Formula (1) to the right side of the formula so asto conduct the washing in a state that the metal colloidal particles areactively agglomerated. Thus salt and a medium can be removed. The metalcolloidal particles that have a sulfuric compound having a low molecularweight, such as mercapto acid, on their surfaces as the dispersant formstable bonds on surfaces of metal. Therefore, if the pH of the solutionis adjusted again to be in an alkaline range that is 6 or more, themetal colloidal particles that are agglomerated are easily dispersedagain, being able to obtain the metal colloidal liquid exhibitingexcellent dispersion stability.

After the above step, it is preferable that an alkali hydroxide metalaqueous solution be added to the aqueous solution in which the silvercolloidal particles are dispersed so as to finally adjust the pH to be 6to 11.

Since the washing is conducted after the reduction, the concentration ofsodium that is an electrolyte ion is sometimes decreased. In thesolution in such state, the equilibrium of the reaction expressed in thefollowing Formula (2) shifts to the right side of the formula. In suchstate, the electrical repulsion of the silver colloid is decreased, sothat the dispersibility of the silver particles is decreased. Therefore,the equilibrium of the reaction expressed in Formula (2) is shifted tothe left side of the formula by adding an appropriate amount of alkalihydroxide, stabilizing the silver colloid.—COO⁻Na⁺+H2O→—COOH+Na⁺+OH⁻  Formula (2)

The alkali hydroxide metal used here may be a compound same as thecompound used when the pH is first adjusted, for example.

In the case of a pH that is less than 6, the equilibrium of the reactionexpressed in Formula (2) shifts to the right side of the formula, makingthe colloidal particles unstable. On the other hand, if a pH exceeds 11,hydroxide salt of remaining ions such as a metal ion unfavorablyprecipitates with ease. Here, if the metal ion is removed in advance,the pH exceeding 11 does not affect largely.

Cations such as sodium ions are preferably added in the form of ahydroxide. This is because self protolysis of water can be used so as tobe able to most effectively add the cations such as sodium ions to thesolution.

By adding other components such as sorbitol and the polyglycerolcompound described above to the aqueous solution, obtained as above, inwhich the silver colloidal particles are dispersed, a conductive patternforming ink (the conductive pattern forming ink of the first embodiment)is obtained.

The addition timing of other components such as sorbitol and thepolyglycerol compound is not especially limited. Other components may beadded anytime after the silver colloidal particles are formed.

Third Embodiment

Conductive Pattern

A conductive pattern according to a third embodiment of the inventionwill now be described.

The conductive pattern is formed by applying the ink described above onthe ceramic formed body and then heating the ceramic formed body so asto have a thin film shape. On the conductive pattern, the silverparticles are bonded to each other. The silver particles are bonded toeach other with no space therebetween at least on the surface of theconductive pattern.

Especially, the conductive pattern is formed by using the conductivepattern forming ink of the first embodiment, so that disconnectioncaused by discharge defects, contact between the conductive patternsthat are adjacent to each other, and the like are prevented.Accordingly, the conductive pattern is homogenized without cracks anddisconnections so as to be highly reliable.

The conductive pattern of the third embodiment is formed such that theink described above is applied on the ceramic formed body by the dropletdischarge method to form a pattern (precursor), then the formed patternis dried (the aqueous dispersion medium is removed) and sintered.

As the drying condition, the drying is preferably conducted at 40degrees Celsius to 100 degrees Celsius, for example, more preferably 50degrees Celsius to 70 degrees Celsius. Such condition can moreeffectively prevent the occurrence of cracks when the ink is dried. Thesintering is conducted at 160 degrees Celsius or more for 20 minutes ormore. The sintering of the precursor can be conducted together withdegreasing and sintering of the ceramic formed body.

The specific resistance of the conductive pattern is preferably lessthan 20 μΩcm, more preferably 15 μΩcm or less. The specific resistancehere is a specific resistance after the ink is applied, heated at 160degrees Celsius, and dried. If the specific resistance becomes 20 μΩcmor more, it becomes hard to use the pattern for a purpose requiringconductivity, that is, to use the pattern for an electrode and the likeformed on a circuit substrate.

In forming the conductive pattern of the third embodiment, a conductivepattern having a large film thickness can be formed by repeating thefollowing steps: applying the ink by the droplet discharge method,pre-heating the ink so as to evaporate the dispersion medium such aswater, and applying the ink on a film after undergoing the pre-heating.

The polyglycerol compound and the silver colloidal particles remain inthe ink after the dispersion medium such as water is evaporated, so thatthe pattern does not flow even in a state that the pattern formed is notcompletely dried. Therefore, after the ink is once applied, dried, andleft for long periods of time, the ink can be applied again.

In addition, the polyglycerol compound described above is chemically andphysically stable. Therefore, even if the ink is left for long periodsof time after applied and dried, the ink does not change in quality,whereby the ink can be applied again. Thus a homogeneous pattern can beformed. Therefore, the conductive pattern is not formed as a multilayerstructure, so that the increase of the specific resistance, which iscaused by the increase of the specific resistance between layers, of thewhole of the conductive pattern does not occur.

Through the above-described steps, the conductive pattern of theembodiment can be formed thicker than a conductive pattern formed from arelated art ink. In particular, a pattern having the thickness of 5 μmor more can be formed. The conductive pattern of the embodiment isformed from the ink described above. Therefore, even if the pattern isformed to have the thickness of 5 μm or more, the pattern hardly hascracks and has low specific resistance. The upper limit of the thicknessis not especially limited. However, if the thickness is too large, thespecific resistance may disadvantageously increase due to the difficultyof removing the aqueous dispersion medium, the polyglycerol compound,and the like. Therefore, the thickness is preferably about 100 μm orless.

Further, the conductive pattern of the embodiment has favorableadhesiveness with respect to the substrate described above.

The conductive pattern described above is applicable to a high frequencymodule of mobile communications equipment such as mobile phones and apersonal digital assistant (PDA); an interposer; micro electromechanical systems (MEMS); an acceleration sensor; a surface acousticwave element; a dissimilar electrode such as antennas and comb-teethelectrodes; and electronic components of various types of measurementapparatuses, for example.

Fourth Embodiment

Wiring Substrate and Method for Manufacturing Wiring Substrate

A wiring substrate (ceramic circuit substrate) including a conductivepattern formed from the conductive pattern forming ink of the firstembodiment and an example of a method for manufacturing the same willnow be described.

A wiring substrate according to a fourth embodiment of the invention isused as an electronic component for various electronic apparatuses. Thewiring substrate has circuit patterns including various wiring lines andelectrodes, laminated ceramic capacitors, laminated inductors, LCfilters, composite high frequency components and the like that areformed on.

FIG. 1 is a longitudinal sectional view showing an example of the wiringsubstrate (ceramic circuit substrate) according to the fourthembodiment. FIG. 2 schematically shows manufacturing steps forexplaining the method for manufacturing the wiring substrate (ceramiccircuit substrate) shown in FIG. 1. FIGS. 3A and 3B are explanatorydiagrams for the manufacturing steps for the wiring substrate (ceramiccircuit substrate) shown in FIG. 1. FIG. 4 is a perspective viewschematically showing a configuration of an ink-jet device (dropletdischarge device). FIG. 5 is a schematic diagram for explaining anoutline configuration of an inkjet head (droplet discharge head).

Referring to FIG. 1, this ceramic circuit substrate (wiring substrate) 1includes a laminated substrate 3 and a circuit 4. The laminatedsubstrate 3 is composed of a number of ceramic substrates 2 (e.g. fromabout 10 to 20 sheets) that are laminated. The circuit 4 includes a finewiring line and the like and formed on an outermost layer of thelaminated substrate 3, i.e., one of surfaces of the laminated substrate3.

The laminated substrate 3 is provided with a circuit (conductivepattern) 5 formed from the conductive pattern forming ink (hereinafter,simply referred to as “ink”) between the ceramic circuit substrates 2that are laminated.

Further a contact (via hole) 6 is formed between the circuits 5 so as tocouple the circuits 5 with each other. In this configuration, thecontact 6 electrically couples the circuits 5 disposed one above theother. Further, likewise the circuit 5, the circuit 4 is formed from theconductive pattern forming ink of the first embodiment.

Now, a method for manufacturing the ceramic circuit substrate 1 will bedescribed with reference to the diagram schematically showing themanufacturing steps in FIG. 2.

First, a ceramic powder made of alumina (Al₂O₃), titanium oxide (TiO₂)or the like having an average particle diameter of about from 1 μm to 2μm and a glass powder made of borosilicate glass or the like having anaverage particle diameter of from about 1 μm to 2 μm are prepared as rawpowders and mixed in an appropriate mixing ratio such as a weight ratioof 1:1, for example.

Then, a binder (binding agent), a plasticizer, an organic solvent(dispersant), and the like are appropriately added to the obtained mixedpowder and followed by mixing and agitating, providing a slurry. Here,polyvinyl butyral is preferably used as the binder. Polyvinyl butyral isinsoluble in water, but soluble in an oil-based organic solvent or easyto swell.

The obtained slurry is formed in a sheet-like shape on a PET film byemploying a doctor blade, a reverse coater, or the like so as to be asheet having a thickness of several micrometers to several hundredmicrometers based on manufacturing conditions of a product. Thereafter,the sheet is rolled up.

Subsequently, the sheet is cut as usage of the product, and further,trimmed in a predetermined size. In the fourth embodiment, the sheet iscut out in a square shape having a side length of 200 mm, for example.

Then, a through hole is formed at a predetermined position by using CO₂laser, YAG laser, a mechanical puncher or the like as necessary.

The through hole is filled with a thick-film conductive paste havingmetal particles dispersed therein, forming a portion to be the contact6. Further, the thick-film conductive paste is applied by screenprinting so as to form a terminal portion (not illustrated) at apredetermined position. Resulting from forming the contact and theterminal portion as above, a ceramic green sheet (ceramic formed body) 7is obtained. As the thick-film conductive paste, the conductive patternforming ink of the first embodiment can be used.

Then, a precursor of the circuit 5, which is the conductive pattern ofthe invention, is continuously formed from the contact 6 on one of thesurfaces of the ceramic green sheet 7 obtained as above. That is, asshown in FIG. 3A, a conductive pattern forming ink (hereinafter, alsosimply referred to as “ink”) 10 as described above is applied on theceramic green sheet 7 by a droplet discharge (ink-jet) method, thusforming a precursor 11 that becomes the circuit 5.

In the fourth embodiment, the conductive pattern forming ink isdischarged with an ink-jet device (droplet discharge device) 50 shown inFIG. 4 and an ink-jet head (droplet discharge head) 70 shown in FIG. 5,for example. The ink-jet device 50 and the ink-jet head 70 will now bedescribed below.

FIG. 4 is a perspective view illustrating the ink-jet device 50. In FIG.4, an X direction is the right-and-left direction of a base 52, a Ydirection is the back and forth direction, and a Z direction is the upand down direction.

The ink-jet device 50 includes the ink-jet head (hereinafter, simplyreferred to as “head”) 70 and a table 46 on which a substrate S (theceramic green sheet 7 in the fourth embodiment) is to be placed. Anoperation of the ink-jet device 50 is controlled by a control unit 53.

The table 46 on which the substrate S is to be placed is allowed to moveand to be positioned in the Y direction by a first moving unit 54, andis allowed to oscillate and to be positioned in a θz direction by amotor 44.

On the other hand, the head 70 is allowed to move and to be positionedin the X direction by a second moving unit (not illustrated), and isallowed to move and to be positioned in the Z direction by a linearmotor 62. Further, the head 70 is allowed to be oscillated and alignedin α, β, and γ directions, respectively by motors 64, 66, and 68. Theink-jet device 50 configured as above is designed so as to preciselycontrol a relative position and posture between an ink dischargingsurface 70P of the head 70 and the substrate S on the table 46.

Further, on the back surface of the table 46, a rubber heater (notillustrated) is provided. The rubber heater heats the entire uppersurface of the ceramic green sheet 7 placed on the table 46 up to apredetermined temperature.

After the ink 10 lands on the ceramic green sheet 7, at least part of anaqueous dispersion medium in the ink 10 evaporates from the surface.Here, since the ceramic green sheet 7 is heated, the evaporation of theaqueous dispersion medium is accelerated. Then, the ink 10 landed on theceramic green sheet 7 increases its viscosity from the outer edge of thesurface as it is dried. That is, the concentration of solid matter(particles) in the outer circumference reaches a saturated concentrationfaster than that in the center portion, so that the ink 10 increases itsviscosity from the outer edge of the surface. The ink 10 having theviscosity increased at the outer edge stops itself from spreading alongthe surface direction of the ceramic green sheet 7, thereby facilitatinga control of a landed diameter, and further facilitating a control of aline width.

A heating temperature here employs the same condition for dryingdescribed above.

The head 70 discharges the ink 10 from a nozzle (protrusion) 91 by anink-jet method (droplet discharge method) as shown in FIG. 5.

As the droplet discharge method, various known techniques can beapplied. Examples of the droplet discharge method include apiezoelectric method in which an ink is discharged using a piezo elementas a piezoelectric element, and a method in which an ink is dischargedby a bubble that is generated by heating the ink. Among these methods,the piezoelectric method has an advantage such as that the compositionof an ink is not affected because no heat is applied to the ink. Thus,the piezoelectric method described above is adopted for the head 70shown in FIG. 5.

A main body 90 of the head 70 includes a reservoir 95 and a plurality ofink chambers 93 that is divaricated from the reservoir 95. The reservoir95 serves as a flow channel to supply the ink 10 into each of the inkchambers 93.

On the bottom surface of the main body 90, a nozzle plate (notillustrated) constituting an ink discharge surface is attached. In thenozzle plate, a plurality of nozzles 91 for discharging the ink 10 isopened corresponding to each of the ink chambers 93. Then, an ink flowchannel is formed toward the corresponding nozzle 91 from each of theink chambers 93. In contrast, a vibrating plate 94 is attached to thetop surface of the main body 90. The vibrating plate 94 constitutes awall surface of each of the ink chambers 93. At the outer side of thevibrating plate 94, a piezo element 92 is disposed correspondingly toeach of the ink chambers 93. The piezo element 92 is formed such that apiezoelectric material such as quartz crystal is interposed between apair of electrodes (not illustrated). The pair of electrodes is coupledto a drive circuit 99.

When an electrical signal is inputted from the drive circuit 99 to thepiezo element 92, the piezo element 92 is deformed and expanded ordeformed and contracted. When the piezo element 92 is deformed andcontracted, the pressure in the ink chamber 93 is lowered, causing theink 10 to flow into the ink chamber 93 from the reservoir 95. Incontrast, when the piezo element 92 is deformed and expanded, thepressure in the ink chamber 93 is increased, causing the ink 10 to bedischarged from the nozzle 91. The deformation amount of the piezoelement 92 can be controlled by changing a voltage to be applied.Further, the deformation speed of the piezo element 92 can be controlledby changing the frequency of the voltage to be applied. That is,discharging conditions of the ink 10 can be controlled by controllingthe voltage applied to the piezo element 92.

Therefore, the ink-jet device 50 provided with the head 70 as aboveallows the ink 10 to be accurately discharged in a desired amount at adesired position on the ceramic green sheet 7. Further, since theconductive pattern forming ink of the first embodiment is used as theink 10, the ink 10 is prevented from being dried in the head 70, thuspreventing metal particles from being separated out. Therefore, theprecursor 11 is accurately and easily formed as shown in FIG. 3A.

After the precursor 11 is formed as above, the ceramic green sheet 7will be formed in a required number, for example, about 10 to 20 sheets,through the same steps.

Subsequently, PET films are removed from those ceramic green sheets andthe ceramic green sheets are layered as shown in FIG. 2, providing alaminated body 12. Here, the ceramic green sheets 7 to be laminated arearranged so that the precursors 11 are coupled to one another asnecessary through the contract 6 between the ceramic green sheets 7disposed one above the other. Thereafter, the ceramic green sheets 7 arebonded to each other with a pressure while being heated at a temperaturemore than or equal to a glass-transition temperature of a binderincluded in the ceramic green sheets 7. The laminated body 12 is thusobtained.

Then, the laminated body 12 formed as above is subjected to heattreatment with a belt furnace or the like, for example. The ceramicgreen sheets 7 are thus sintered and form the ceramic substrates 2 (thewiring substrate of the fourth embodiment) as shown in FIG. 3B. Further,silver colloidal particles in the precursor 11 are sintered, therebyforming the circuit (conductive pattern) 5 including wiring patterns andelectrode patterns. The laminated body 12 processed through the heattreatment as above serves as the laminated substrate 3 shown in FIG. 1.

Here, the temperature to heat the laminated body 12 is preferably morethan or equal to a softening temperature of glass included in theceramic green sheet 7, that is, more specifically, from 600 to 900degrees Celsius inclusive. Further, as the heating conditions, thetemperature is increased or decreased at an appropriate speed, andfurther, maintained for an appropriate period of time depending on thehighest heating temperature, that is, the temperature from 600 to 900degrees Celsius as above.

A glass component in the ceramic substrate 2 that is obtained can bethus softened by increasing the heating temperature up to the softeningtemperature of the glass, that is, the temperature range describedabove. Therefore, by cooling down the glass component to a roomtemperature so as to be hardened, the ceramic substrate 2 and thecircuit (conductive pattern) 5 that constitute the laminated substrate 3are further firmly bonded to each other.

Further, by heating the laminated body 12 in the temperature range asabove, the ceramic substrate 2 that is obtained becomes a lowtemperature co-fired ceramic (LTCC) that is formed by being sintered at900 degrees Celsius or less.

Here, metal particles included in the ink 10 deposited on the ceramicgreen sheet 7 are fused and continuously coupled to each other by theheat treatment, thereby exhibiting electrical conductivity.

Through the heat treatment as above, the circuit 5 is formed to bedirectly coupled with the contact 6 in the ceramic substrate 2, andelectrically conducted. Here, if the circuit 5 is simply placed on theceramic substrate 2, the circuit 5 cannot securely have mechanicalconnection strength with the ceramic substrate 2, and thus may bedamaged on impact or the like. However, in the fourth embodiment, theglass included in the ceramic green sheet 7 is softened once and thenhardened as described above, allowing the circuit 5 to firmly bond tothe ceramic substrate 2. Therefore, the circuit 5 that is formed canalso have mechanically high strength.

Through the heat treatment as above, the circuit 4 is concurrentlyformed with the circuit 5, thus providing the ceramic circuit substrate1.

In the method for manufacturing the ceramic circuit substrate 1 asabove, in particular, since the ink 10 (the conductive pattern formingink of the invention) described above is deposited on the ceramic greensheet 7 in the manufacturing step for the ceramic substrate 2constituting the laminated substrate 3, the conductive pattern formingink 10 is favorably deposited on the ceramic green sheet 7 in a desiredpattern. Therefore, the conductive pattern (circuit) 5 with highaccuracy is formed.

While the preferred embodiments of the invention have been described,they are not intended to limit the invention.

For example, in the embodiments, a case where a colloidal liquid is usedas a dispersion liquid in which metal particles are dispersed in asolvent has been described, however, the dispersion liquid is notnecessarily the colloidal liquid.

Further, in the embodiments described above, a case where the conductivepattern forming ink includes silver particles dispersed therein has beendescribed, however, the conductive pattern forming ink may include metalparticles other than silver particles. Examples of metals included inthe metal particles include silver, copper, palladium, platinum, andgold or their alloys. These may be used singly or in combination of twoor more. When the metal particles are made of an alloy, the alloy mayinclude metals other than the above as long as a metal among the metalsdescribed above is used as a main constituent of the alloy. Further, analloy made of the metals described above mixed with each other at anarbitrary ratio may be used. Furthermore, a liquid including mixedparticles (e.g. silver particles, copper particles, and palladiumparticles are included at an arbitrary ratio) dispersed therein may beused. These metals have small resistivity and are stable because of notbeing oxidized by heat treatment. Therefore, using the metals can form astable conductive pattern having low resistivity.

For example, in the embodiments, a case where the conductive patternforming ink is applied to the ceramic formed body and sintered so as toform a ceramic substrate and a conductive pattern has been described,however, substrates other than the above may be used. As the substrateused for forming the conductive pattern is not particularly limited.Examples of materials for the substrate includes a ceramic sinteredbody, an alumina sintered body, polyimide resin, phenol resin, glassepoxy resin, glass, and the like. Alternatively, the conductive patternforming ink may be directly applied on a ceramic substrate.

WORKING EXAMPLES

Hereinafter, the invention will be described in further detail by usingworking examples, but the invention is not limited to the examples.

[1] Preparation of Conductive Pattern Forming Ink

Each of conductive pattern forming inks of Examples and ComparativeExamples is produced as below.

Examples 1 to 11

In 50 mL of water that was alkalified by adding 3 mL of a 10N-NaOHaqueous solution, 17 g of trisodium citrate dihydrate and 0.36 g oftannic acids were dissolved. Then, 3 mL of a 3.87 mol/L silver nitrateacid aqueous solution was added to the obtained solution and agitatedfor 2 hours, thus providing a silver colloidal liquid. The silvercolloidal liquid having been obtained was desalinated until itselectrical conductivity became 30 μS/cm or less through dialysis. Afterthe dialysis, bulky metal colloidal particles were removed bycentrifugal separation under conditions of 3000 rpm for 10 minutes.

To the silver colloidal liquid, sorbitol, a polyglycerol compound shownin Table 1, Surfynol 104PG50 (by Air Products and Chemicals, Inc.) andOlfine EXP4036 (by Nissin Chemical Industry Co., Ltd) that serve as anacetylene glycol based compound were added. When a pH of the silvercolloidal liquid was not in a range from 6 to 11, the pH of the silvercolloidal liquid was adjusted to be in the range from 6 to 11 by using a1N-NaOH aqueous solution. Further, ion-exchanged water for concentrationadjustment was added to the silver colloidal liquid, thus providing theconductive pattern forming ink.

Example 12

While 1000 mL of a 50 mmol/L silver nitrate acid aqueous solution wasbeing agitated, 3.0 g of mercaptoacetic acid as a sulfuric compoundhaving a low molecular weight was added thereto. Thereafter, a pH of theaqueous solution was adjusted to 10.0 by adding 26 wt % ammonia water.Then, under room temperature, 50 mL of a 400 mmol/L sodium borohydrideaqueous solution was rapidly added to the aqueous solution above so asto produce a reduction reaction, forming the silver colloidal particleshaving particle surfaces covered with mercaptoacetic acid in thesolution.

The colloidal liquid obtained as above was adjusted to pH 3.0 by using20 wt % nitric acid. After the silver colloidal particles settled out,the colloidal liquid was filtered with a vacuum filter so as to separatethe particles from the colloidal liquid and the particles were washedwith water until the electrical conductivity of the filtrate became 10.0μS/cm or less, thus providing a wet cake of the silver colloidalparticles.

The wet cake of the silver colloidal particles was added to water sothat its concentration was 10 wt %, and was adjusted to pH 9.0 by adding26 wt % ammonia water while being agitated. The silver colloidalparticles were re-dispersed and then the liquid was concentrated,providing a silver colloidal liquid.

A conductive pattern forming ink was prepared as below in the samemanner as in Example 1.

Comparative Example 1

A conductive pattern forming ink was produced in the same manner asExample 1 except for not adding the sorbitol.

Comparative Example 2

A conductive pattern forming ink was produced in the same manner as inExample 1 except for not adding the polyglycerol compound.

Comparative Examples 3 and 4

A conductive pattern forming ink was produced in the same manner asExample 1 except for that the contents of the polyglycerol compound andthe sorbitol were changed as shown in Table 1.

Comparative Example 5

A conductive pattern forming ink was produced in the same manner asExample 1 except for that the polyglycerol compound was not added andthe content of sorbitol was changed as shown in Table 1.

Comparative Example 6

A conductive pattern forming ink was produced in the same manner asExample 1 except for that the sorbitol was not added and the content ofthe polyglycerol compound was changed as shown in Table 1.

Compositions of the conductive pattern forming inks according toExamples and Comparative Examples are shown in Table 1. In Table 1, acontent of each material indicates an amount contained in the conductivepattern forming ink. X(A)[wt %] represents the content of thepolyglycerol compound in the conductive pattern forming ink, whileX(B)[wt %] represents the content of the sorbitol in the conductivepattern forming ink. Further, “H” represents the H in the formula Idescribed above. OH(A) represents the number of hydroxyl groups in onemolecule of the polyglycerol compound, while OH(B) represents the numberof hydroxyl groups in one molecule of the sorbitol. Mw(A) represents aweight-average molecular weight of the polyglycerol compound, whileMw(B) represents a molecular weight of the sorbitol. Furthermore, “A”represents polyglycerol #500 (a weight-average molecular weight of 462),“B” represents polyglycerol #300 (a weight-average molecular weight of312), “C” represents polyglycerol #400 (a weight-average molecularweight of 370), “D” represents polyglycerol #800 (a weight-averagemolecular weight of 759), and “E” represents polyglycerol #3000 (aweight-average molecular weight of 3000).

TABLE 1 Silver Colloidal particles Content of Acetylene glycol SilverPolyglycerol compound Sorbitol based compound 1,3- Colloidal Content OHContent Surfynol Olfine propanediol Water particles X (A) Mw (A) X (B)Mw OH (B) 104PG50 EXP4036 Content Content X (A)/ [wt %] Type [wt %] (A)[piece] [wt %] (B) [piece] [wt %] [wt %] [wt %] [wt %] X (B) H Example 140.0 A 9.0 462 8 6.0 182 6 0.02 0.006 5.0 40.0 1.50 0.35 Example 2 40.0A 18.0 462 8 4.5 182 6 0.02 0.006 5.0 32.5 4.00 0.46 Example 3 40.0 A2.8 462 8 21.0 182 6 0.02 0.006 5.0 31.2 0.13 0.74 Example 4 40.0 A 0.8462 8 23.0 182 6 0.02 0.006 5.0 31.2 0.03 0.77 Example 5 40.0 A 20.0 4628 2.0 182 6 0.02 0.006 5.0 33.0 10.00 0.41 Example 6 40.0 A 26.0 462 81.5 182 6 0.02 0.006 5.0 27.5 17.33 0.50 Example 7 40.0 A 2.8 462 8 5.3182 6 0.02 0.006 5.0 46.9 0.53 0.22 Example 8 40.0 B 9.0 312 6 6.0 182 60.02 0.006 5.0 40.0 1.50 0.37 Example 9 40.0 C 9.0 370 7 6.0 182 6 0.020.006 5.0 40.0 1.50 0.37 Example 10 40.0 D 9.0 759 12 6.0 182 6 0.020.006 5.0 40.0 1.50 0.34 Example 11 40.0 E 9.0 3000 22 6.0 182 6 0.020.006 5.0 40.0 1.50 0.26 Example 12 40.0 A 9.0 462 8 6.0 182 6 0.020.006 5.0 40.0 1.50 0.35 Comparative 40.0 A 9.0 462 8 — — — 0.02 0.0065.0 46.0 — 0.16 Example 1 Comparative 40.0 — — — — 6.0 182 6 0.02 0.0065.0 49.0 — 0.20 Example 2 Comparative 40.0 A 11.0 462 8 20.0 182 6 0.020.006 5.0 24.0 0.55 0.85 Example 3 Comparative 40.0 A 3.0 462 8 2.5 1826 0.02 0.006 5.0 49.5 1.20 0.13 Example 4 Comparative 40.0 — — — — 14.0182 6 0.02 0.006 5.0 41.0 — 0.46 Example 5 Comparative 40.0 A 25.0 462 8— — — 0.02 0.006 5.0 30.0 — 0.43 Example 6

[2] Producing Ceramic Green Sheet

First, a ceramic green sheet (ceramic formed body) was prepared asfollows.

A ceramic powder made of alumina (Al₂O₃), titanium oxide (TiO₂) or thelike having an average particle diameter of about from 1 μm to 2 μm anda glass powder made of borosilicate glass or the like having an averageparticle diameter of from about 1 μm to 2 μm were mixed at a weightratio of 1:1. Then, polyvinyl butyral serving as a binder (bindingagent), and dibutylphthalate serving as a plasticizer were added to themixture, and then the resulting mixture was mixed and agitated,providing a slurry. The resulting slurry was formed in a sheet-likeshape on a PET film by employing a doctor blade as a ceramic greensheet, and the sheet was cut into a square having a side length of 200mm to be used.

[3] Evaluation of Ink Storage Stability

Right after being produced, each of the conductive pattern forming inksobtained in Examples and Comparative Examples was dropped one each on aglass substrate and left under an atmosphere at a temperature of 25degrees Celsius and a humidity of 60%. After being left, each of theconductive pattern forming inks having been dropped was examined whetherkeeping a liquid state or not by inserting a glass rod into the ink. Thenumber of days until the ink was not able to keep a liquid state afterthe ink was left was evaluated as a liquid state period based oncriteria at 4 levels.

A: Liquid state period is 30 days or more.

B: Liquid state period is 9 days or more and less than 30 days.

C: Liquid state period is 3 days or more and less than 9 days.

D: Liquid state period is less than 3 days.

[4] Evaluation of Droplet Discharge Stability

Right after being produced, each of the conductive pattern forming inksobtained in Examples and Comparative Examples was filled into an inkjetdevice similar to the one shown in FIGS. 4 and 5. First, after drawingwith the ink-jet device including the conductive pattern forming ink asabove was conducted, it was confirmed that the ink was stablydischarged. Then, the inkjet device was left in a standby state in whichthe inkjet head was out of a drawing position in a Class 100 clean roomenvironment at a room temperature of 25 degrees Celsius and a respectivehumidity of 60% for 5 days. Next, the ink-jet device was turned on andallowed to draw a solid pattern on 20 of ceramic green sheets that wereobtained as above. When the ink discharge was unstable, the inkdischarge was recovered to a stable state by using a predeterminedcleaning mechanism installed in the ink-jet device. After the aboveoperations, the discharge stability was evaluated based on the followingevaluation criteria.

-   -   A: Ink is stably discharged without nozzle clogging during        drawing (excellent discharge stability).    -   B: Cleaning operation is required twice or less to obtain stable        ink discharge after nozzle clogging during drawing (no problems        in practical use).    -   C: Cleaning operation is required three times or more to obtain        stable ink discharge after nozzle clogging during drawing        (practically usable).    -   D: Nozzle clogging occurred during drawing is not recovered by        cleaning operation (not suitable for practical use).

Further, the same evaluation was performed in a case where the sameoperations were carried out after the standby state of 30 days.

[5] Production and Evaluation of Wiring Substrate

Each of the conductive pattern forming inks obtained in Examples andComparative Examples was supplied to a droplet discharge device similarto the one shown in FIGS. 4 and 5.

Then, the ceramic green sheets described above were heated to andmaintained at 60 degrees Celsius. Droplets each of which was 15 ng weresubsequently discharged from each discharge nozzle so as to draw 20lines (precursor) having a line width of 45 μm, a thickness of 15 μm,and a length of 10.0 cm. A distance between the lines was set to be 5mm. Then, the ceramic green sheets having the lines formed thereon wereloaded in a drying furnace and heated under the conditions at 60 degreesCelsius for 30 minutes so as to be dried.

The ceramic green sheets having the lines formed thereon according tothe above were regarded as first ceramic green sheets. With each of theinks, 20 of the first ceramic green sheets were formed. Further, each ofthe sheets was examined whether it had cracks or not. The results arelisted in Table 2. Table 2 shows the number of nondefective ceramicsheets having no cracks in the lines among the first ceramic greensheets.

Next, in another ceramic green sheet, through holes with a diameter of100 μm were formed at both edges of the metal wiring lines by punchingwith a mechanical puncher or the like, thus forming 40 through holes intotal. The through holes were filled with each of the conductive patternforming inks obtained in Examples and Comparative Examples, therebyforming contacts (via holes). Further, a pattern having a 2 mm squarewas formed on the contact (via hole) by using each of the conductivepattern forming inks obtained in Examples and Comparative Examples withthe droplet discharge device so as to form a terminal portion.

The ceramic green sheets having the terminal portion formed thereon wereregarded as second ceramic green sheets.

Then, one of the first ceramic green sheets was laminated under one ofthe second ceramic green sheets. Further, two ceramic green sheets thathave not been processed were laminated thereto as a reinforcement layer,thereby providing a raw laminated body. Then, 20 blocks of the rawlaminated body were formed for each of the inks so as to correspond toevery one of 20 of the first ceramic green sheets.

Then, the raw laminated body was pressed with a pressure of 300 kg/cm2at 90 degrees Celsius for 45 seconds. Thereafter, the raw laminated bodywas sintered based on a sintering profile in which the raw laminatedbody was continuously heated at a rate of temperature rise of 64 degreesCelsius per hour for about 5 hours, at a rate of temperature rise of 15degrees Celsius per hour for about 6 hours, and at a rate of temperaturerise of 90 degrees Celsius per hour for about 5 hours, and after theelevated temperature process, was maintained at a highest temperature of885 degrees Celsius for 30 minutes. A ceramic circuit board was thusobtained.

After being cooled down, each ceramic circuit substrate was subjected toa check on conductivity by placing a tester between terminal portionsformed on 20 of the conductive patterns. A ceramic circuit substratehaving 100% electrical conductivity was regarded as a non-defectivesubstrate. Here, the electrical conductivity was obtained by dividingthe number of conductive patterns having electrical conductivity in eachof the ceramic circuit substrates by the number of conductive patterns(20 patterns) having been formed.

The results are shown in Table 2.

[Table 2]

TABLE 2 Number of non- Number defectives of non- Droplet discharge afterdefectives stability drawing after Storage 5-day 30-day and dryingsintering stability period period [piece] [piece] Example 1 A A A 20 20Example 2 A A B 19 19 Example 3 A A A 20 18 Example 4 B B B 18 15Example 5 A A A 16 13 Example 6 B B C 12 10 Example 7 A A A 18 10Example 8 A A A 17 16 Example 9 A A A 20 20 Example 10 A A A 20 20Example 11 A B B 16 14 Example 12 A A A 20 20 Comparative D B D 6 3Example 1 Comparative B A A 12 2 Example 2 Comparative A A A 14 5Example 3 Comparative D B D 12 4 Example 4 Comparative A A A 14 4Example 5 Comparative B D D 4 3 Example 6

As shown in Table 2, all the conductive pattern forming inks of theinvention attained the excellent storage stability and dischargestability.

Further, as shown in Table 2, the ceramic circuit substrate having linesformed by using each of the conductive pattern forming inks ofComparative Examples had many cracks in the lines, and further, thelines themselves likely lost their shapes after drawing and drying inproducing the ceramic circuit substrate. On the other hand, the ceramiccircuit substrate having lines formed by using each of the conductivepattern forming inks of Examples hardly had cracks in the lines.Further, compared to the cases of the Comparative Examples, obviously,the lines were maintained without loosing their shapes.

Further, as shown in Table 2, at a disconnection check with the testerafter the ceramic circuit substrates having lines formed by using eachof the conductive pattern forming inks of Comparative Examples wassintered, electrical conductivity between the lines was hardlyconfirmed. On the contrary, the ceramic circuit substrate having linesformed by using each of the conductive pattern forming inks of Exampleshad a large number of lines exhibiting conductivity, thereby providingthe metal wiring lines that were extremely favorable. Resulting fromexamining the conductivity failures, it was confirmed that theconductivity failures were caused by cracks, and disconnections occurredduring the sintering.

Further, when the content of the silver colloidal particles in the inkswas changed to 20 wt % and 30 wt %, the same results as above wereobtained.

What is claimed is:
 1. A conductive pattern forming ink for forming aconductive pattern on a substrate by a droplet discharge method,comprising: metal particles; an aqueous dispersion medium in which themetal particles are dispersed; sorbitol; and a polyglycerol compoundhaving a polyglycerol skeleton, wherein H shown in the following Formula(I) is 0.20 to 0.80; $\begin{matrix}{H = {{\frac{{OH}(A)}{{Mw}(A)}{X(A)}} + {\frac{{OH}(B)}{{Mw}(B)}{X(B)}}}} & {{Formula}\mspace{14mu}(I)}\end{matrix}$ wherein OH(A) represents an average number of hydroxylgroups in one molecule of the polyglycerol compound, Mw(A) represents aweight-average molecular weight of the polyglycerol compound, X(A)represents the content of the polyglycerol compound in the conductivepattern forming ink in weight percent; and OH(B) represents a number ofhydroxyl groups in one molecule of the sorbitol, Mw(B) represents amolecular weight of the sorbitol, and X(B) represents a content of thesorbitol in the conductive pattern forming ink in weight percent.
 2. Theconductive pattern forming ink according to claim 1, wherein the X(A)and the X(B) satisfy a relation of 0.5≦X(A)/X(B)≦15.
 3. The conductivepattern forming ink according to claim 1, wherein the X(A) is 1.0 wt %to 25 wt %.
 4. The conductive pattern forming ink according to claim 1,wherein the X(B) is 3.0 wt % to 23 wt %.
 5. The conductive patternforming ink according to claim 1, wherein the polyglycerol compound ispolyglycerol.
 6. The conductive pattern forming ink according to claim1, wherein the Mw(A) is 300 to
 3000. 7. The conductive pattern formingink according to claim 1, wherein a total content of the sorbitol andthe polyglycerol compound in the conductive pattern forming ink is 4.0wt % to 50 wt %.
 8. The conductive pattern forming ink according toclaim 1, wherein the substrate is formed by degreasing and sintering aceramic formed body made of a material containing ceramic particles anda binder so as to have a sheet like shape, and the conductive patternforming ink is applied to the ceramic formed body by the dropletdischarge method.
 9. The conductive pattern forming ink according toclaim 1, wherein the conductive pattern forming ink is a colloidalliquid in which metal colloidal particles composed of the metalparticles and a dispersant adsorbing onto surfaces of the metalparticles is dispersed in the aqueous dispersion medium.
 10. Theconductive pattern forming ink according to claim 9, wherein thedispersant includes one of hydroxy acid and salt of hydroxy acid thathaving in total three or more of at least one COOH group and at leastone OH group, and a number of COOH groups is equal to or larger than anumber of OH groups.
 11. The conductive pattern forming ink according toclaim 9, wherein the dispersant includes one of mercapto acid and saltof mercapto acid having in total two or more of at least one COOH groupand at least one SH group.
 12. The conductive pattern forming inkaccording to claim 9, wherein the colloidal liquid has a pH of 6 to 11.13. A conductive pattern formed from the conductive pattern foil lingink according to claim
 1. 14. A wiring substrate provided with theconductive pattern according to claim 13.